1. Field of the Invention
The present invention relates to a technique for recording dots on the surface of a recording medium with the aid of a dot-recording head, and more particularly to a technique for printing images while accurately positioning the printing paper.
2. Description of the Related Art
Inkjet printers have recently become popular as computer output devices. FIG. 27 is a side view depicting the periphery of a print head for a conventional inkjet printer. Printing paper P is fed in the direction of arrow A by the upstream paper feed rollers 25p and 25q disposed upstream of a platen 26o and by the downstream paper peed rollers 25r and 25s disposed downstream of the platen 26o, and is stopped at specific positions. The printing paper P is supported on the platen 26o while facing the head 28o. Numerous ink droplets Ip are ejected from the print head in the direction of a specific position on the platen 26o while the printing paper is advanced in small increments in the direction of arrow A. The ink droplets Ip are deposited on the printing paper P on the platen 26o, and images are recorded on the printing paper.
In such printers, images cannot be formed at the intended positions on the printing paper when the printing paper shifts away from the intended position, which is shown by a broken line in FIG. 27. In addition, the image initially designed to be formed near the edges of the printing paper sometimes ends up extending beyond the printing paper. In such cases, the ink droplets end up missing the initially targeted edge portions of the printing paper, deposit on the platen, and soil the printing paper transported over the platen in the next step, as shown in FIG. 27.
It is an object of the present invention to overcome the above-described shortcomings of the prior art and to provide a technique for printing images while accurately positioning the printing paper.
The present invention envisages adopting the following structure in order to at least partially overcome the above-described shortcomings. This dot-recording device records ink dots on a surface of a print medium with the aid of a dot-recording head provided with a plurality of dot-forming elements for ejecting ink droplets. This dot-recording device comprises: a main scanning unit configured to move the dot recording head relative to the print medium to perform main scanning; a head drive unit configured to drive at least some of the plurality of dot-forming elements to form dots during the main scanning; a sub-scanning unit configured to move the print medium to perform sub-scanning in a sub-scanning direction; a sensor for detecting presence of the print medium at a specific detection point; and a controller configured to control the dot-recording device. The sensor is disposed at a point outside paths of the ink droplets ejected by the plurality of dot-forming elements during the main scanning. Adopting such an embodiment allows the print medium to be accurately positioned, dots to be recorded, and images to be formed on the print medium by detecting the presence of the print medium with the sensor.
The dot-recording device should preferably print images in the following manner. A sub-scan feed is started from a state in which the print medium is absent from the detection point, the sub-scanning being a scanning operation for driving the print medium across the main scanning direction. The sub-scan feed of the print medium is stopped at a specific position of sub-scanning associated with a position where the sensor detects the presence of the print medium. Main scanning is started and ink droplets are ejected from the dot-forming elements after the print medium reaches the specific position of sub-scanning. Printing images in this manner allows the print medium to be positioned by a method in which the arrival of the leading edge of the print medium to a specific detection point is used as reference.
It is preferable that the sensor comprises: a light emitter configured to emit light to the detection point; and a light receiver configured to receive the light reflected by the print medium. With this arrangement, the print medium can be detected by a noncontact technique, and dots can be recorded unimpeded on the print medium.
It is preferable that the sensor is configured to be moved together with the dot-recording head during the main scanning. Adopting such an embodiment removes any interference between the sensor and the dot-recording head during the main scanning.
It is preferable that the sensor is provided proximate to a dot-forming element position along the sub-scanning direction. The dot-forming element is located at a downstream and in the sub-scanning direction among the dot-forming elements used for printing. Adopting such an embodiment allows the presence of a print medium to be detected and the print medium to be positioned in the vicinity of dot-forming elements for printing images along the front edge of the print medium. The; print medium can therefore be accurately positioned relative to the dot-forming elements for printing images along the leading edge of the print medium.
The printing device preferably further comprises a platen configured to support the print medium that is extending in the main scanning direction and is disposed opposite the dot-forming elements at least along part of a main scan path. The platen has a downstream slot extending in the main scanning direction. The downstream slot is disposed at a position opposite a dot-forming element that is located at a downstream end in the sub-scanning direction. The detection point is located inside the downstream slot and within a sub-scanning range containing the plurality of dot-forming elements. Adopting such an embodiment makes it possible to determine that the leading edge of a print medium has reached the opening of the downstream slot, and to allow the dot-forming elements to start recording dots near the leading edge of the print medium.
According to this embodiment, the platen is provided with a lateral slot connected to the downstream slot and is disposed at least in the area in which ink droplets are deposited from the plurality of dot-forming elements in the sub-scanning direction. In addition, the following structure should preferably be adopted. The platen further has a lateral slot. The lateral slot is connected to the downstream slot and extending in a sub-scanning range in which ink droplets are ejected from the plurality of dot-forming elements. The dot-recording device further comprises a guide configured to guide the print medium to be at a specific position in the main scanning direction during the sub-scanning, the specific position being where the print medium is in a main scanning range in which the dot-recording head is moved and where one of side edges of the print medium is above the lateral slot. The detection point is in the area of connection of the lateral slot and the downstream slot. Adopting such an embodiment makes it possible to start recording dots on the print medium upon determining that the leading edge of the print medium is disposed at the opening of the downstream slot and that the side edges are disposed above the openings of the lateral slots.
It is preferable that the lateral slot comprises first and second lateral slots. The first and second lateral slots are configured such that the side edges of the print medium are above the first and second lateral slot when the print medium is set at the specific position. With such an embodiment, one of the side edges of the print medium is disposed above the opening of the second lateral slot when it is determined that the leading edge of the print medium is disposed at the opening of the downstream slot and the other side edge is disposed above the openings of the first lateral slot. The recording of dots on the print medium can be started when the existence of such an arrangement is confirmed.
It is preferable that the sensor is positioned upstream in the sub-scanning direction of a dot-forming element that is located on a downstream end in the sub-scanning direction among the dot-forming elements used for dot recording. Adopting this arrangement allows dots to be formed on a print medium at least by the dot-forming elements disposed along the downstream end in the sub-scanning direction without reversing the sub-scanning after the rear edge of the print medium has been detected by the sensor.
The printing described as follows may be performed in the dot recording device that has the sensor that is disposed upstream or in the vicinity in the sub-scanning direction of a dot-forming element that is located on the downstream end in the sub-scanning direction among the dot-forming elements used for dot recording. In the printing, image data is prepared that allow images to be printed in an image area comprising an area on the print medium and an area extending beyond the rear edge of the print medium. Dot recording is performed according to the image data while performing the main scanning and sub-scanning. The sensor detects the rear edge of the print medium on the detection point. The dot recording is continued according to the image data until the sub-scanning is performed for a predetermined distance after the detecting, to thereby complete the dot recording on the print medium. Adopting this arrangement allows images to be printed by confirming that the rear edge of the print medium has moved past a specific detection position, allowing images to be printed at exact positions in front or behind the rear edge of the print medium.
The dot-recording device should preferably comprise a storage unit for storing the number of main scan lines in which images are to be freshly recorded by main scanning while ink droplets are ejected after the sensor can no longer detect the presence of the print medium. Adopting this arrangement allows images to be printed at exact positions in front or behind the rear edge of the print medium by feeding the print medium in the sub-scanning direction according to the pre-stored feed amount(that is the predetermined distance.)
The number of main scan lines (or the predetermined distance) designated for recording new images after the sensor can no longer detect the presence of the print medium should preferably be established in accordance with material of the print medium. Adopting this arrangement makes it possible to increase the total value of feeding during sub-scanning when the print medium is made of a material characterized by increased slippage during sub-scanning, and to reduce the total value of feeding during sub-scanning when the print medium is made of a material characterized by reduced slippage during sub-scanning.
It is preferable that the predetermined distance depends on size of the print medium. Adopting this arrangement makes it possible to increase the total value of feeding (the predetermined distance) during the sub-scanning of a large print medium, and to reduce the total value of feeding during the sub-scanning of a small print medium.
A dot-recording device preferably further comprises a platen configured to support the print medium. The platen is extending in the main scanning direction, is disposed opposite the dot-forming elements at least along part of a main scan path and has a slot. The is slot extending in the main scanning direction. The width of the slot in the sub-scanning direction corresponding to a specific sub-scanning range on a surface of the dot recording head including at least part of the plurality of dot-forming elements. The detection point is preferably located inside the slot and within a sub-scanning range containing the plurality of dot-forming elements. Adopting this arrangement makes it possible to confirm that the leading edge or the rear edge of the print medium has reached the slot opening, and to record dots on the print medium with the aid of the dot-forming elements disposed opposite the slot.
It is preferable that the slot is an upstream slot extending in the main scanning direction and is disposed at a position opposite a dot-forming element that is located at a upstream edge in the sub-scanning direction. Adopting this arrangement makes it possible to form dots on the rear edge of the print medium over the upstream slot by employing at least the dot-forming elements disposed on the upstream edge in the sub-scanning direction. It is therefore possible to achieve a smooth transition from printing images in the middle portion of the print medium to printing images on the rear edge thereof without resorting to reverse feeding when nozzles other than those disposed opposite the slot are used to print images in the middle portion of the print medium.
The sensor may also be proximate to a slot-facing, dot-forming element position along the sub-scanning direction. The dot-forming element is located on the downstream end. Adopting this arrangement makes it possible to print images by confirming that the rear edge of the print medium has moved past the dot-forming elements used for image printing and disposed opposite the slot. It is thus possible to reduce the area in which ink droplets are ejected beyond the edges of a print medium.
The present invention can be implemented as the following embodiments.
(1) A dot-recording method, print control method, or printing method.
(2) A dot-recording device, print control device, or printing device.
(3) A computer program for operating the device or implementing the method.
(4) A storage medium containing computer programs for operating the device or implementing the method.
(5) A data signal carried by a carrier wave and designed to contain a computer program for operating the device or implementing the method.